1. Field of the Invention
The invention relates to a pneumatic-spring percussion mechanism for an impact hammer and/or drill hammer.
2. Description of the Related Art
Among the currently conventional types of percussion mechanism for drill hammers or impact hammers, the design which has proven successful, in particular, is one in which a drive piston designed as a hollow piston is made to move axially in an oscillating manner via a crank mechanism. A solid percussion piston is moved in the interior of the drive piston, which is guided in the housing of the hammer, said percussion piston projecting at the open end of the hollow drive piston and acting cyclically on a cutter tool or an interposed riveting set. A pneumatic spring is formed for this purpose in a cavity between the percussion piston and the drive piston, said pneumatic spring transmitting the forced movement of the drive piston to the percussion piston and driving the latter against the tool.
The percussion mechanism takes up a comparatively small amount of space and can be produced cost-effectively. Furthermore, the percussion system reaches a high impact speed. The reliable start-up of the percussion mechanism from idling is also particularly advantageous.
The disadvantage, however, is the high mass of the drive piston, since the latter is moved back and forth by the drive even during idling, i.e. in a state in which the tool is not working on any materials. The comparatively large oscillating masses render the hammer more difficult to handle during idling.
U.S. Pat. No. 3,456,740 discloses a percussion mechanism with a double-acting pneumatic spring. Provided in a drive piston is an air-equalizing slot over which a percussion piston which can be moved back and forth in the interior of the drive piston can pass such that alternately the front and the rear pneumatic springs are brought into connection with the surroundings. As a result, the pneumatic springs are recharged after each blow. However, such double pneumatic-spring percussion mechanisms require a large amount of space and cannot be operated in idling mode.
EP 0 014 760 A1 describes a pneumatic-spring mechanism with a hollow drive piston in which a percussion piston is driven by a pneumatic spring which forms between the drive piston and the percussion piston. When the hammer in which the percussion is used is raised from the rock which is to be worked, the percussion piston is displaced forward to such an extent that the pneumatic spring can be brought into connection with the surroundings via an idling bore. The refilling of the pneumatic spring in percussion operation takes place via a radial bore in a guide sleeve of the drive piston, which is activated via a stationary slot.
The object of the invention, while maintaining the positive features of the percussion mechanism, is to achieve a reduction in the vibrations occurring during idling.
The object is achieved according to the invention by a pneumatic-spring percussion mechanism according to claim 1. Advantageous configurations of the pneumatic-spring percussion mechanism are defined in the subclaims.
The pneumatic-spring percussion mechanism according to the invention has a drive piston which has a piston-suspension means, a piston head and a guide sleeve, at least one air-equalizing slot being provided in the guide sleeve. It is possible for the guide sleeve to be of hollow-cylindrical design or to be elliptical or to have a number of sides.
A preferred embodiment is defined in that the air-equalizing slot extends in the axial direction of the guide sleeve. It is particularly advantageous, therefore, for the guide sleeve to have the smallest possible wall thickness, of less than 5% of the diameter of the guide sleeve, and to be provided with idling openings.